In panel display technology, organic light-emitting diode (OLED) displays have characteristics of thinness, self-luminosity, fast response times, wide viewing angles, wide color gamut, high brightness, low energy consumption, and many other advantages, and have gradually become a third generation display technology after liquid crystal display technology. Compared to liquid crystal displays (LCDs), OLEDs have advantages of lower energy consumption, thinner, and wide viewing angles, which are incomparable for conventional LCDs. At present, detail degree requirements (i.e. resolution) are getting higher and higher. However, production of high-quality, high-resolution OLED displays still has many challenges.
A core component of an OLED display device is an OLED display panel. An OLED display panel film structure is shown as FIG. 1. The OLED display panel includes a thin film transistor layer 101 and an anode layer, a pixel definition layer 102, a first common layer 103, a light emitting layer, a second common layer 104, and a cathode layer 105 formed on a TFT substrate in sequence.
The OLED display panel works by an electric field between an anode and a cathode, holes are transmitted through the first common layer 103 to the light emitting layer, electrons are transmitted to the light emitting layer through the second common layer 104. The holes and the electrons recombine and then emit light within the light emitting layer.
The OLED display panel is usually used for displaying different colors by a combination of R, G, B three primary colors. Thus, one pixel of the OLED display panel typically contains three light emitting units of R, G, and B colors. In actual use, we require the light emitting units of R, G, and B colors of each pixel can be controlled by a drive circuit individually.
As a resolution of the display panel increases, a number of the light emitting units per unit area increases, thereby resulting in a decrease in distance between the light emitting units. Light emitting layers of the light emitting units of R, G, and B colors are made of different materials, and turn-on voltages of the light emitting units of R, G, and B colors are also different. In manufacturing the OLED display panel, it can be seen that since adjacent light emitting units can communicate with each other through the first common layer 103 and the distance between the light emitting units is small, a few amount of the holes can be injected into the second light emitting unit through the first common layer 103 and are recombined with the electrons in a second light emitting unit to emit light when a first light emitting unit is turned on in a condition of low current. Because the first light emitting unit emits weak light at low current and an influence is generated by a light emission of the second light emitting unit, result is that the first light emitting unit emits impurity. This luminescence phenomenon is called light leakage, and current generated by leakage of a few amount of holes is called leakage current.
For example, it is assumed that the turn-on voltages of the light emitting units of R, G, and B colors are R>G>B.
1. When an R picture is lit at a voltage slightly higher than an R turn-on voltage, a few amount of holes will pass through the first common layer 103 to an interface of adjacent the light emitting units of G and B. Since the R turn-on voltage is greater than a G turn-on voltage and a B turn-on voltage, the holes can enter into the light emitting units of G and B and recombine with the electrons to emit light.
2. When a G picture is lit at a voltage slightly higher than a G turn-on voltage, a few amount of holes will pass through the first common layer 103 to an interface of adjacent the light emitting units of R and B. Since the G turn-on voltage is greater than a B turn-on voltage, the holes can enter into the light emitting unit of B and recombine with the electrons to emit light. The G turn-on voltage is lower than the R turn-on voltage, the holes cannot enter into the light emitting unit of R, and thereby R cannot emit light.
3. When a B picture is lit at a voltage slightly higher than the B turn-on voltage, a few amount of holes will pass through the first common layer 103 to an interface of adjacent the light emitting units of R and G. Since the B turn-on voltage is lower than the R turn-on voltage and the G turn-on voltage, the holes cannot enter the light emitting units of R and G, R and G cannot emit light. That is, when R and G are lit at low current individually, it may cause the adjacent light emitting units to emit light, thereby leading to uneven light emission.
In addition, when R is lit at a high current, a few amount of holes can provide for light emitting units of G and B for emitting light. However, brightness is relatively weak and is covered by a strong light emitted by the light emitting unit of R. The light emitted by the light emitting units of G and B cannot be identified by human eyes.
Thus, the leakage is generally more obvious in a situation of low current and the leakage will reduce display effect of the OLED display panel.